Multi-mode address mapping management

ABSTRACT

In one aspect of multi-mode address mapping management in accordance with the present disclosure, mapping and unmapping operations may be conducted in one of multiple address mapping management modes to both improve overall system performance and maintain data integrity. In one embodiment, a first address mapping management mode such as a rigorous mode, for example, confirms completion of an unmapping of an address mapped data unit buffer before a re-mapping is permitted. Mapping and unmapping operations may be switched to a performance mode in which unmap completion confirmation is bypassed to improve performance. In one embodiment, address mapping management modes may be switched in real time as a function of monitored operating conditions. Other aspects and advantages are provided, depending upon the particular application.

BACKGROUND 1. Field of the Invention

The present invention relates to a computer program product, computersystem, and computer-implemented method for multi-mode address mappingmanagement in a data storage system.

2. Description of the Related Art

A storage system may control access to storage for one or more hostcomputational devices that may be coupled to the storage system over anetwork. A storage management application that executes in the storagesystem may manage a plurality of storage devices, such as disk drives,tape drives, flash drives, direct access storage devices (DASD), etc.,that are coupled to the storage system. A job executing on a host maysend Input/Output (I/O) commands or requests to the storage system whichexecutes the I/O requests to read data from the storage devices or writedata to the storage devices. The storage system typically includes astorage controller which controls the storage devices.

A storage controller of a storage system may include two or moreservers, where each server may be referred to as a node, a storageserver, a processor complex, a Central Processor Complex (CPC), or aCentral Electronics Complex (CEC), for example. Each server may beincluded in a cluster. Each server may have a plurality of processorcores and the servers may share the workload of the storage system. In atwo server configuration of the storage system referred to as adual-server storage controller, either server can failover to the otherif there is a failure or a planned downtime for one of the two servers.A hypervisor provides various supervisory services to the servers suchas address mapping services, for example.

A cache is a memory which typically provides faster access to data forinput/output operations as compared to storage. Data to be read may befirst staged into the cache from storage and then read directly from thecache instead of directly from the storage to provide faster access toread data. Conversely, data to be updated may be first updated in thecache and then destaged to storage which is typically non-volatilestorage, that is, the data persists in the non-volatile storagenotwithstanding a loss of power to the storage. By comparison, some orall of the cache memory may be volatile memory, that is, data may notpersist in a volatile cache in the event of a power failure.

In one known system, the storage system attempts to maintain two copiesof the data while data is moving through the storage system. The serverseach have two areas of their primary memory that are used for holdinghost data: cache and non-volatile storage (NVS). NVS contains write datauntil the data is safely destaged from the cache to the storage drives.When a write is sent to a volume and both the servers are operational,the write data is placed into the cache of the owning server and intothe NVS of the other server. The NVS copy of the write data may beaccessed if a write failure occurs and the cache is empty or possiblyinvalid in the owning server. Otherwise, the NVS copy of the write datamay be discarded after the destage from cache to the storage drives iscomplete.

Each server of the storage system typically has a number of hostadapters which couple the storage system to a one or more hosts. Eachserver of the storage system also has a number of device adapters whichcouple the servers of the storage system to storage such as an array ofdisk drives, for example. The host adapters and device adapters aretypically connected to processors of the servers by one or more bussessuch as a Peripheral Component Interconnect Express (PCIe) bus, forexample. In one known design, data transfers between an adapter at oneend and the cache or the NVS of a server at the other end isaccomplished by direct memory access (DMA) transfers over a PCIe bus. Tofacilitate the DMA transfer, a range of addresses of a source or targetadapter on the PCIe bus, referred to as a PCIe window, may be mapped bythe hypervisor to physical addresses of a cache or the NVS. Morespecifically, the PCIe window associated with an adapter may be mappedto cache memory addresses of segments of a track in a cache, or to NVSmemory addresses of segments of a track buffer of the NVS. The PCIewindow mapped to a cache or NVS location, points to addresses of theadapter to which data may be transferred from or transferred to in a DMAtransfer.

In one known system, the hypervisor provides mapping tables such astranslation control entry (TCE) tables maintained in a cache of thehypervisor, to translate addresses for the PCIe mapping. By calling ahypervisor service, a server program can cause the creation,modification, or deletion of TCE table entries in the hypervisor cachefor the specific PCIe adapters assigned to that server. For example,upon completion of a DMA transfer, the mapping of a PCIe window to anassociated cache track or NVS track buffer is unmapped by calling ahypervisor service “dkill” which clears the hypervisor cache of TCEtable entries for mappings which are to be unmapped.

However, performance and completion of the dkill service may be delayedbecause the hypervisor is otherwise busy or occupied with other tasks.Accordingly, a known hypervisor dkill service sets a completionindication control register to indicate completion of the dkill cacheclearance and thus completion of the unmapping of the selected PCIewindow and selected NVS track buffer used for a completed DMA transfer.The hypervisor periodically polls this control register in an unmapcompletion polling, to check its status. If unmap completion pollingdetermines that the control register has been set, the hypervisorreports to the requesting server that the requested dkill service andthus the requested unmapping, have been completed. Upon receipt ofconfirmation of completion of the requested dkill service and unmapping,the server can safely initiate another mapping. In this manner, correctmapping and unmapping of PCIe windows and NVS track buffers isfacilitated.

However, unmap completion polling by the hypervisor and associatedwaiting for completion of unmapping can cause a significant degradationin system performance. Accordingly, in one known system, unmapcompletion polling by the hypervisor to check for completion ofhypervisor cache clearance can be removed from the system to improvesystem performance.

SUMMARY

In accordance with certain embodiments, addresses for a selected dataunit buffer of a storage controller and a selected adapter coupled tothe storage controller, are mapped in a selected address mappingmanagement mode, for a first data transfer between an address mappeddata unit buffer and an address mapped adapter of the first datatransfer. In one aspect, upon completion of the first data transfer,unmapping of the address mapped data unit buffer and the address mappedadapter of the first data transfer, is initiated in the selected addressmapping management mode. In response to the selected address mappingmanagement mode being in a first address mapping management mode such asa rigorous mode, for example, the initiated unmapping of the addressmapped data unit buffer and the address mapped adapter of the first datatransfer is confirmed as complete prior to again initiating anotheraddress mapping a selected data unit buffer of the storage controllerand a selected adapter coupled to the storage controller, for a seconddata transfer between an addressed mapped data unit buffer and anaddress mapped adapter.

In another aspect, in response to the selected address mappingmanagement mode being in a second address mapping management mode suchas a performance mode, for example, another address mapping of aselected data unit buffer of the storage controller and a selectedadapter coupled to the storage controller is initiated, for a seconddata transfer between an addressed mapped data unit buffer and anaddress mapped adapter, without confirming that the initiated unmappingof the address mapped data unit buffer and the address mapped adapter ofthe first data transfer is complete. As a result, confirming that theinitiated unmapping of the address mapped data unit buffer and theaddress mapped adapter of the first data transfer is complete, isbypassed prior to again initiating address mapping a selected data unitbuffer of the storage controller and a selected adapter.

In still another aspect, selecting an address mapping management modeincludes monitoring the level of free data unit buffers available for anadditional data transfer wherein data unit buffers are freed aftercompletion of data transfers to those data unit buffers to be availablefor an additional data transfer to each free data unit buffer. The levelof free data unit buffers is compared to a first threshold level such asa relatively low threshold level, for example. In response todetermining that the level of free data unit buffers is below the firstthreshold level, selecting the first address mapping management mode.

In yet another aspect, selecting an address mapping management modeincludes monitoring the level of free data unit buffers available for anadditional data transfer, and comparing the level of free data unitbuffers to a second threshold level such as a relatively high thresholdlevel. In response to determining that the level of free data unitbuffers is above the second threshold level, selecting the secondaddress mapping management mode.

Another aspect of multi-mode address mapping management in accordancewith the present description, is directed to determining the currentselected address mapping management mode in response to determining thelevel of free data unit buffers to be above the second threshold level.In response to determining that the current selected address mappingmanagement mode is the first address mapping management mode, starting atimer to start timing a first wait period prior to selecting the secondaddress mapping management mode.

In one embodiment, a determination is made as to whether the level offree data unit buffers remains above the second threshold level duringthe first wait period. In response to determining that the level of freedata unit buffers remains above the second threshold level during thefirst wait period, the second address mapping management mode isselected. Alternatively, in response to determining that the level offree data unit buffers has fallen below the second threshold levelduring the first wait period, the first address mapping management modeis continued.

Yet another aspect is directed to restarting the timer to start timing asecond wait period in response to determining that the level of freedata unit buffers has fallen below the second threshold level during thefirst wait period. In addition, a determination is made during thesecond wait period as to whether the level of free data unit buffersrises above the second threshold level. In response to determining thatthe level of free data unit buffers remains above the second thresholdlevel during the second wait period, the second address mappingmanagement mode is selected. Conversely, in response to determining thatthe level of free data unit buffers has fallen below the secondthreshold level during the second wait period, the first address mappingmanagement mode is continued.

Still another aspect is directed to an address mapped adapter beingassociated with a particular data transfer and being coupled to one of astorage and a host so that the particular data transfer transfers databetween the one of the storage and host coupled to the associatedaddress mapped adapter, and an address mapped data unit bufferassociated with the particular data transfer.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, like reference numbers represent corresponding partsthroughout.

FIG. 1 illustrates, in a block diagram, a computing environmentemploying multi-mode address mapping management in accordance withcertain embodiments.

FIG. 2 depicts an example of I/O workload sharing in connection with afirst cache and a first NVS controlled by a first server, and a secondcache and a second NVS controlled by a second server, in accordance withcertain embodiments.

FIG. 3 illustrates, in a block diagram, host adapters and deviceadapters for the servers of the storage controller of FIG. 1.

FIG. 4 illustrates, in a flowchart, an example of operations formulti-mode address mapping management in accordance with certainembodiments.

FIGS. 5a, 5b depict examples of mappings and unmappings for adapter buswindows and cache in the computer environment of FIG. 1.

FIGS. 6a, 6b, 6c depict examples of mappings and unmappings for adapterbus windows and NVS in the computer environment of FIG. 1.

FIG. 7 illustrates, in a flowchart, another example of operations formulti-mode address mapping management in accordance with certainembodiments.

FIG. 8 illustrates, in a block diagram, a computer system employingmulti-mode address mapping management in accordance with certainembodiments.

DETAILED DESCRIPTION

The descriptions of the various embodiments of multi-mode addressmapping management in accordance with the present disclosure, have beenpresented for purposes of illustration, but are not intended to beexhaustive or limited to the embodiments disclosed. Many modificationsand variations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

As noted above, a requested dkill service for unmapping an addressmapping may be delayed while the hypervisor is busy with other tasks. Inknown systems, in order to determine when the dkill service hascompleted cleaning the hypervisor cache to unmap prior mappings, thehypervisor periodically polls a control register which is set uponcompletion of the dkill service, to check the status of that register.However, such unmap completion polling by the hypervisor can cause asignificant degradation in system performance. Accordingly, in one knownsystem, unmap completion polling by the hypervisor can be removed fromthe system to improve system performance. However, it is appreciatedherein that such an improvement in performance may have an associatedincreased risk of incorrect mapping or unmapping of an NVS track buffer,for example, and a resultant data loss in some circumstances.

In one aspect of multi-mode address mapping management in accordancewith the present disclosure, the mapping and unmapping(mapping/unmapping) operations of the hypervisor may be conducted in oneof multiple address mapping management modes to both improve overallsystem performance and maintain data integrity. In one embodiment, thehypervisor may be operated in a first address mapping management mode,referred to herein as a rigorous mode, in which completion of anunmapping for an NVS track buffer is assured by unmap completion pollingbefore a re-mapping of the same NVS track buffer is permitted.

As explained in greater detail below, the rigorous mode may be utilizedas conditions warrant to prevent loss of data integrity, albeit withsome potential performance degradation. However, in one aspect ofmulti-mode address mapping management in accordance with the presentdisclosure, it is recognized that as operational conditions change, therigorous mode may no longer be appropriate or needed to ensure dataintegrity. Accordingly, the hypervisor may be switched in real time to asecond address mapping management mode, referred to herein as aperformance mode. In the performance mode, re-mapping of the same NVStrack buffer is permitted without first confirming that unmapping of theprior mapping of that NVS track buffer has been completed. As a result,unmap completion polling may be bypassed in the performance mode toimprove system performance without increasing the risk of data loss, asconditions warrant.

Thus, in one embodiment, operating conditions may be monitored and theaddress mapping management mode of the hypervisor may be automaticallyswitched back and forth in real time between the rigorous andperformance modes as appropriate to increase overall system performancewhile maintaining data integrity in both modes. In one embodiment, anNVS manager provides an indication to the hypervisor in the form of a“hint” as to which address mapping management mode to utilize based uponan analysis of current operating conditions.

For example, it is recognized herein that if data transfer operationsselect from available NVS track buffers in a sequential fashion such asa round robin sequence, for example, and that the I/O workload is lowsuch that there is an adequate supply of available track buffers, anyone NVS track buffer for which unmapping has previously been requested,will likely not be selected again for a relatively long interveningperiod of time. Accordingly, if the unmapping of a particular NVS trackbuffer did not complete in response to the dkill service requested tounmap that particular NVS buffer, it is appreciated that subsequentdkill service requests to unmap other NVS track buffers in theintervening period are likely to complete the unmapping of theparticular NVS track buffer as well. Accordingly, a performance mode maybe employed which bypasses unmap completion polling operations employedby the rigorous mode to improve system performance when I/O workload issufficiently low.

Conversely, if the I/O workload is sufficiently high, it is appreciatedthat an unmap completion polling operation of the rigorous mode may beappropriate to ensure that the unmapping has been completed beforeproceeding to the next mapping. For example, it is recognized hereinthat if the I/O workload is relatively high such that the supply ofavailable NVS track buffers is relatively low, any one NVS track bufferfor which unmapping has previously been requested, has an increasedlikelihood of being selected again in a relatively short interveningperiod of time.

Accordingly, if the unmapping of a particular NVS track buffer did notcomplete in response to the dkill service previously requested to unmapthat particular NVS buffer, it is appreciated that there may be aninsufficient number of subsequent dkill service requests to unmap otherNVS track buffers in the intervening period to ensure completion of theunmapping of the particular NVS track buffer as well. Accordingly, inhigh I/O workload conditions, the current address mapping managementmode may employ the rigorous mode such that unmap completion polling ofthe rigorous mode is utilized. As a result, in the rigorous mode,operations do not proceed to the next mapping without first waiting forthe prior unmapping to complete. In this manner, data integrity may bepreserved notwithstanding relatively high levels of I/O workload.

Thus, in one embodiment, address mapping management operations mayswitch back and forth between the rigorous mode and the performance modeautomatically and in real time as a function of the level of the I/Oworkload, for example. It is appreciated that the level of I/O workloadmay be monitored and measured using a variety of techniques for purposesof selecting an appropriate address mapping management mode as afunction of I/O workload level. In one embodiment, the number of freeNVS track buffers may be monitored and an address mapping managementmode may be selected as a function of the current number of free NVStrack buffers. It is appreciated that address mapping management modesmay be selected as a function of other criteria, depending upon theparticular application.

A system of one or more computers may be configured for multi-modeaddress mapping management in accordance with the present description,by virtue of having software, firmware, hardware, or a combination ofthem installed on the system that in operation causes or cause thesystem to perform with multi-mode address mapping management inaccordance with the present description. For example, one or morecomputer programs in computer-readable memories may be configured toperform with multi-mode address mapping management by virtue ofincluding instructions that, when executed by data processing apparatussuch as for example a storage controller processor, cause the apparatusto perform the actions.

The operations described herein are performed by logic which isconfigured to perform the operations either automatically orsubstantially automatically with little or no system operatorintervention, except where indicated as being performed manually Thus,as used herein, the term “automatic” includes both fully automatic, thatis operations performed by one or more hardware or software controlledmachines with no human intervention such as user inputs to a graphicaluser selection interface. As used herein, the term “automatic” furtherincludes predominantly automatic, that is, most of the operations (suchas greater than 50%, for example) are performed by one or more hardwareor software controlled machines with no human intervention such as userinputs to a graphical user selection interface, and the remainder of theoperations (less than 50%, for example) are performed manually, that is,the manual operations are performed by one or more hardware or softwarecontrolled machines with human intervention such as user inputs to agraphical user selection interface to direct the performance of theoperations.

Many of the functional elements described in this specification havebeen labeled as “logic,” in order to more particularly emphasize theirimplementation independence. For example, a logic element may beimplemented as a hardware circuit comprising custom VLSI circuits orgate arrays, off-the-shelf semiconductors such as logic chips,transistors, or other discrete components. A logic element may also beimplemented in programmable hardware devices such as field programmablegate arrays, programmable array logic, programmable logic devices or thelike.

A logic element may also be implemented in software for execution byvarious types of processors. A logic element which includes executableprogram code may, for instance, comprise one or more physical or logicalblocks of computer instructions which may, for instance, be organized asan object, procedure, or function. Nevertheless, the executables of anidentified logic element need not be physically located together, butmay comprise disparate instructions stored in different locations which,when joined logically together, comprise the logic element and achievethe stated purpose for the logic element.

Indeed, executable code for a logic element may be a single instruction,or many instructions, and may even be distributed over several differentcode segments, among different programs, among different processors, andacross several memory devices. Similarly, operational data may beidentified and illustrated herein within logic elements, and may beembodied in any suitable form and organized within any suitable type ofdata structure. The operational data may be collected as a single dataset, or may be distributed over different locations including overdifferent storage devices.

FIG. 1 illustrates a block diagram of a computing environment comprisinga storage system 100 which includes storage 101 controlled by a dualcluster storage controller 102. In this embodiment, the storagecontroller 102, which may an IBM Enterprise Storage Server (ESS), forinstance, is a high-capacity device that can back up data from a varietyof different storage devices. For example, a large corporation or otherenterprise may have a network of servers that each store data for anumber of workstations used by individual employees. Periodically, thedata on the host servers is backed up to the high-capacity storagecontroller 102 to avoid data loss if the host servers malfunction. Thestorage controller 102 can also provide data sharing between hostservers since it is accessible to each host server. The storagecontroller 102 itself has redundant storage resources to provide anadditional safeguard against data loss. As a further measure, the dataof the storage controller 102 may be mirrored to another storage server,typically at a remote site. A storage server of a particular type, suchas one that uses disk storage, may connect to one or more other peerdisk storage servers as well as to other storage devices, such as thoseusing magnetic tape. Communication between the devices may be achievedusing any desired communication protocol and medium. A user interfacemay be provided to allow a user to access information regarding thestatus of the storage controller 102.

In this example, the storage controller 102 is a dual cluster systemcomprising a first server 104 and a second server 106, where the storagecontroller 102 communicates with a plurality of hosts 108 . . . 110 overa network 111, in accordance with certain embodiments. A job executingon a host 108, 110 may send Input/Output (I/O) commands or requests tothe storage system 100. Each server 104, 106 includes a storage managerwhich executes the I/O requests to read data from the storage devices101 or write data to the storage devices 101 which store data in volumes120, for example.

The storage controller 102, the servers 104, 106 and the hosts 108, 110may comprise any suitable computational device including those presentlyknown in the art, such as, a personal computer, a workstation, a server,a mainframe, a handheld computer, a palm top computer, a telephonydevice, a network appliance, a blade computer, a processing device, acontroller, etc. The plurality of servers 104, 106 may provideredundancy because if one server undergoes a failure from which recoveryis not possible, an alternate server may perform the functions of theserver that failed. Each of the plurality of servers 104, 106 may bereferred to as a processing complex of a cluster and may include one ormore processors and/or processor cores.

The storage controller 102, the servers 104, 106, the hosts 108, 110 andthe storage 101, may be elements in any suitable network 111, such as, astorage area network, a wide area network, the Internet, an intranet. Incertain embodiments, storage controller 102, the servers 104, 106, thehosts 108, 110 and the storage 101, may be elements in a cloud computingenvironment.

The first server 104 includes memory comprising a first cache 112 and afirst NVS 114, and the second server 106 includes memory comprising asecond cache 116 and a second NVS 118. The caches 112, 116 may becontrolled by cache managers 113, 117, respectively, which are part ofthe respective storage manager of the server 104. Similarly, the NVS's114, 118 may be controlled by NVS managers 115, 119, respectively, whichare part of the storage manager of the server 106. For the purposes ofthis disclosure, operations shown as being performed by a cache areperformed under control of a cache manager 113, 117 and operations shownas being performed by an NVS are performed under control of an NVSmanager 115, 119.

The storage managers including the cache managers 113, 117, the NVSmanagers 115, 119, and a hypervisor 121 execute software, firmwareand/or micro code, e.g., computer code devices, stored in an associatedmemory to achieve the functionality described herein. Such memories maybe considered to be program storage devices. The memories may beprovided, e.g., in a region of the respective cache that is preservedduring a reboot, or in a separate non-volatile memory.

The cache 112, 116 may in certain embodiments, comprise a write cachepartitioned into one or more ranks, where each rank may include one ormore storage tracks. The cache 112, 116 may be any suitable cache knownin the art or developed in the future. In some embodiments, the cache112, 116 may be implemented with a volatile memory and/or non-volatilememory such as a multi-tier cache having a relatively fast cache tierimplemented with DRAM type memory, for example, and a relatively slowcache tier implemented with NAND type flash memory, for example. Thecache 112, 116 may store both modified and unmodified data, where thecache 112,116 may periodically destage (i.e., move) data from the cache112, 116 to storage drives 101 controlled by the servers 104, 106.

The NVS 114, 118 may also be referred to as a “persistent” cache and isimplemented with non-volatile memory that may or may not utilizeexternal power to retain data stored therein. In some embodiments, abackup power source, such as a battery, supplies the NVS 114, 118 withpower to retain the data stored therein in case of power loss. The NVS114, 118 may store modified data. An application is made aware that anI/O operation is complete once data has successfully been written tocache and the NVS. Data integrity and availability is maintained byretaining two copies of the data until it is hardened to disk, one copyin cache on one server and the second in NVS of the other server. NVSmay be protected by battery backup. Normal access to the data is fromthe copy retained in the cache. In certain embodiments, the NVS 114, 118may also act like a write cache.

Generally, if data requested by a host resides in one of the caches 112,116, an immediate data transfer takes place. If the data is not in thecaches, one of the servers 104, 106 sends a request to its deviceadapter to retrieve the data from the disk arrays of the storage 101.When a read operation arrives at a server, a cache hit occurs if therequested data resides in the cache, resulting in better performance. Acache miss occurs if the data is not in the cache. In response to acache miss, a stage operation occurs, which involves reading data from adisk drive of storage 101 into the appropriate cache. The NVS's 114,118, which are battery backed memories or solid state nonvolatilestorage in this embodiment, improve performance by allowing write I/Ooperations to complete after the data is stored in NVS, but before thedata is destaged to the disk arrays of storage 101. If a server fails,the surviving server can access the write data of the failed server inits local NVS. The caches 112, 116 may be volatile memories that are notbattery backed or may include non-volatile storage in some embodiments.

A physical hypervisor (PHYP) 121 is in one embodiment, a component ofsystem firmware of the storage controller 102 and provides capabilitiesto allow one portion of memory of a server to be used as cache andanother portion be used as NVS. The PHYP 121 has a cache 122 and allowsthe contents of the NVS 114, 118 and cache 112, 116 to be protected in a“memory preserve cache” managed by the PHYP 121 in case of a reboot. ThePHYP 121 may execute in any or all of the servers 104, 106. In certainembodiments, the PHYP 121 may be implemented in software, firmware,hardware or any combination thereof, instead of or in addition to beingimplemented in the system firmware.

It should be noted that the storage controller 102 may be configured andaccessed in many different ways. For example, virtualization may beperformed to access the hardware elements of the storage controller 102.Additionally, in certain embodiments, the storage controller 102 mayhave a single server or more than two servers.

The I/O workload of the storage controller 102 may be shared by theservers 104, 106. FIG. 2 depicts one example of such workload sharing inconnection with first cache 112 and the first NVS 114 controlled by thefirst server 104(FIG. 1), and the second cache 116 and the second NVS118 controlled by the second server 106, in accordance with certainembodiments. In this example, the first cache 112 is used for alllogical volumes 120 (FIG. 1) that are members of even numbered logicalstorage systems (LSS) 202. It may be noted that an LSS is a logicalconstruct that groups logical volumes and logical units (LUN) in groups,where in certain embodiments the LSS's may be numbered via integersstarting from 0 to and ending at 255 if there are 256 LSS's. Likewise,the second cache 116 is used for all logical volumes 120 (FIG. 1) thatare members of odd numbered LSS's 204. For every write that is placedinto the first cache 112 of the first server 104, a copy 206 is placedinto the second NVS 118 that is in the second server 106. For everywrite that is placed into the second cache 116 of the second server 106,a copy 208 is placed into the first NVS 114 that is in the first server104. As a result, in case of failure of the first server 104, the secondserver 106 may be used for recovery of data, and in case of failure ofthe second server 106 the first server 104 may be used for the recoveryof data.

In certain embodiments, each track (an exemplary track 210 is shown) mayinclude multiple segments of 4 Kbytes in size. Thus, in this example, atrack is divided into segments of sectors, which may comprise a basicunit of storage. The exemplary track 210 of FIG. 2 has up to 17 segmentsas represented by the segments 212, 214 . . . 216, where a track 210 isallocated to the cache 112, 116 in segments of 4 Kbytes, i.e., a subsetof segments of the track 210 may reside in the cache 112, 116. In asimilar manner, a track buffer may be allocated to an NVS 114, 118 insegments of 4 Kbytes, i.e., a subset of segments of a track buffer mayreside in an NVS 114, 118.

As noted above with respect to FIG. 2, for every write that is placedinto the first cache 112 of the first server 104, a copy is placed intothe NVS 118 that is in the second server 106. Thus, the following normalflow of data is for a write from a host when both the first server 104and the second server 106 are operational:

-   (1) Data is written to cache 112 in the first server 104. At the    same time, data is written to NVS 118 of the second server 106;-   (2) The write operation is reported to the host as completed;-   (3) The write data is destaged from the first cache 112 of the first    server 104 to a storage drive array; and-   (4) The write data is discarded from the NVS 118 of the second    server 106.

Therefore, the cache has both modified and unmodified data for a track,whereas the NVS typically has modified data. When a track gets destagedto a disk, the track is then unmodified, and the track may then bediscarded from the NVS as the NVS only stores modified data in oneembodiment.

Therefore a host writes to both the cache 112 and NVS 118 in parallel. Awrite to cache takes place in two phases. In the first phase trackaccess is taken and the track is associated with a “write in progress”.Then in a second phase the track access ends and the write completes.When a host writes a track into NVS, a commit is performed to indicatethat write is complete.

Referring to FIG. 3, device adapters (DA) 340, 350 are used to connectthe disks of a disk array of the storage 101 to the caches 112, 116 inthe servers 104, 106 (FIG. 1). In one possible design, each server 104,106 is assigned four device adapters 340, 350, respectively. Eachadapter is part of a pair, one on each server. A pair supports twoindependent paths to all of the disk drives served by the pair. Eachdisk array is configured to be accessed by only one of the servers.However, if a server failure occurs, the surviving server automaticallytakes over all of the disks. The disk arrays or ranks of the storage 101can be configured as RAID 5 (redundant array of independent disks) ornon-RAID arrays. Alternatively, another high-capacity storage medium maybe used. The device adapters 340, 350 are connected to the servers 104,106 (FIG. 1) by a suitable bus or network connection. In the illustratedembodiment, PCIe busses 364 a, 364 b connect device adapters 340, 350 toservers 104, 106, respectively. Accordingly data transfers between thedevice adapters 340, 350 and servers 104, 106 take place over the PCIebusses 364 a, 364 b. Although the connections between device adapters340, 350 and servers 104, 106, are described as PCIe busses, it isappreciated that other types of bus or network connections may beemployed, depending upon the particular application.

Host adapters (HA's) 370 are external interfaces that may support twoports, in one embodiment, e.g., either small computer systems interface(SCSI) or IBM's enterprise systems connection (ESCON), which is anEnterprise Systems Architecture/390 and zSeries computer peripheralinterface. In one embodiment, this I/O interface uses ESA/390 logicalprotocols over a serial interface that configures attached units to acommunication fabric of the network 111 (FIG. 1). For example, a remotestorage server, host servers and a user interface may communicate withthe storage controller 102 via the HA's. Fibre channel or Fibre-channelconnection (FICON) has support for one channel per HA. Each HA connectsto both servers 104, 106, so that either server can handle I/Os from anyhost adapter. A system adapter identification number (SAID) is a uniqueidentification number automatically assigned to each HA. The storagecontroller 102 contains four host-adaptor bays, each of which isconnected to both servers 104, 106 for redundancy. In the illustratedembodiment, PCIe bus 364 c connects host adapters 370 to servers 104,106. It is appreciated that other types of bus or network connectionsmay be employed, depending upon the particular application.

A host may have data stored into storage 101 (FIG. 1) via the storagecontroller 102 by issuing a write request to a host adapter 370 (FIG. 3)such as the host adapter 370 a, for example. The write request mayinclude a track identification (ID) which identifies the track for whichthe data is to be stored. In response, the host adapter 370 a receivingthe write request sends mail to the appropriate cache manager for thattrack ID such as the cache manager 113 (FIG. 1), for example, informingthe cache manager 113 of the write request for a particular track IDsuch as track IDO, for example. The location of the track IDO write datawithin the host adapter 370 a is also identified.

FIG. 4 depicts one example of operations 404-428 for which of one ormore of the cache manager 113 (FIG. 1), NVS manager 119 and physicalhypervisor 121 have been configured. In this example, one or more of thecache manager 113 (FIG. 1), NVS manager 119 and physical hypervisor 121have been configured for mapping and unmapping management operations inaccordance with the present description, for transferring write datafrom a host adapter such as the host adapter 370 a, to cache and NVS.Although the logic performing the operations of FIG. 4 are described inconnection with the cache manager 113 (FIG. 1), NVS manager 119 andphysical hypervisor 121 in the illustrated embodiment, it is appreciatedthat logic performing such management operations may be located in fewerdevices or in other devices, depending upon the particular application.

In response to the mail from the host adapter 370 a informing the cachemanager 113 of the write request for a particular track ID such as trackIDO, for example, the cache manager 113 in this example, allocates(block 404, FIG. 4) segments 512a (FIG. 5a ) in the cache 112 for cachetrack IDO. The segments 512 a of cache track IDO are allocated toreceive the write data identified by track identification IDO, in a DMAtransfer (block 408, FIG. 4) by the cache manager 113 of the server 104,from the identified location within the host adapter 370 a to theallocated segments 512 a (FIG. 5a ) for the cache track IDO of the cacheaddress space 516 of the cache 112 (FIG. 1) of the server 104. In theillustrated embodiment, the identified location of the write data forthe cache track IDO within the host adapter 370 a (FIG. 3), correspondsto a PCIe window identified as adapter bus window 520 a (FIG. 5a ) inthis example, of the adapter bus address space 524. As explained ingreater detail below, to facilitate the DMA transfer of the write datato the cache track IDO of the cache 112 from the host adapter 370 a, thecache manager 113 causes the physical hypervisor 121 (FIG. 1) to map(block 404, FIG. 4) in a mapping 528 a (FIG. 5a ), the adapter buswindow 520 a to the allocated segments 512 a for the cache track IDO asrepresented by an address mapping arrow in FIG. 5 a.

As previously mentioned, data writes to the cache 112 of the server 104are also written to the NVS 118 of the other server 106 to provide abackup in the event the write data in the cache 112 is lost before ithas been committed to storage 101. More specifically, for each write toa cache track in the cache 112, the same data is written to a trackbuffer in the NVS 118. Once the write data has been safely destaged fromthe cache track to the storage 101, the write data in the correspondingtrack buffer of the NVS 118 may be discarded, freeing the allocatedsegments of that track buffer for use for another data write. In someembodiments, the NVS 118 may support up to 4000 track buffers, forexample. These track buffers may be used in a round robin fashion, forexample, cycling through the available track buffers by selecting thenext available track buffer in sequence.

Accordingly, in response to the mail from the host adapter 370 ainforming the cache manager 113 of the requested write to the cache 112,the cache manager 113 also requests the NVS manager 119 to allocate(block 404, FIG. 4) segments 604 b (FIG. 6a ) in the NVS 118 of the NVSaddress space 608, for an available track buffer such as the trackbuffer0, for example. However, for reasons of system performance, theallocation of segments 604 b for the track buffer0 is for the next datatransfer using the NVS track buffer0 rather than for the currenttransfer to the NVS track buffer0. Instead, the current DMA datatransfer will utilize the segments 604 a which were previously allocatedfor the track buffer0 in connection with a prior data transfer.

The NVS allocated segments 604 a for the current data transfer to thetrack buffer0 receive the write data identified by track identificationIDO, in a DMA transfer (block 408, FIG. 4) by the NVS manager 119 of theserver 106 from the identified location within the host adapter 370 a tothe segments 604 a allocated for the track buffer0 of the NVS addressspace 608. As previously mentioned, in this example, the identifiedlocation of the write data for track identification IDO within the hostadapter 370 a, corresponds to the PCIe window identified as adapter buswindow 520 a in this example, of the adapter bus address space 508. Tofacilitate the DMA transfer (block 408, FIG. 4) of the IDO write datafrom the host adapter 370 a to the NVS track buffer0, the cache manager113 and/or the NVS manager 119 informs the physical hypervisor 121 thatthe NVS destination of the IDO write data is the NVS track buffer0 andcauses the physical hypervisor 121 (FIG. 1) to map in a mapping 628 a(FIG. 6a ), the adapter bus address window 520 a to the segments 604 apreviously allocated for the current data transfer to the NVS trackbuffer0, as represented by an address mapping arrow (FIG. 6a ), asexplained in greater detail below. Although described herein inconnection with a DMA transfer in the illustrated embodiment, it isappreciated that data transfers between adapters and cache and NVSmemory may be accomplished through any suitable data transfer procedure.

Upon completion (block 412) of the DMA transfers to the cache track IDOand to the NVS track buffer0, the cache manager 113 and/or the NVSmanager 119 frees (block 416, FIG. 4) the track buffer0 for use foranother data transfer and initiates unmapping the mappings 528 a, 628 a.In this embodiment, the hypervisor 121 provides mapping tables such astranslation control entry (TCE) tables to translate addresses for themapping. By calling a hypervisor service, a server program can cause thecreation, modification, or deletion of TCE table entries for thespecific PCI adapters assigned to that server. Thus in this example, thecache manager 113 and/or the NVS manager 119 can cause the hypervisor121 to create suitable TCE table entries to implement the mappings 528a, 628 a (block 408, FIG. 4) by calling a suitable hypervisor TCEservice. In a similar manner, the cache manager 113 and/or the NVSmanager 119 can initiate (block 416, FIG. 4) the unmapping of themappings 528 a, 628 a by calling a dkill hypervisor service to cause thehypervisor 121 to delete the TCE table entries for the mappings 528 a,628 a, by clearing those TCE table entries from the hypervisor cache122.

However, it is appreciated herein that performance and completion of thedkill service may be delayed because the hypervisor 121 is otherwisebusy or occupied with other tasks. In one aspect of multi-mode addressmapping management in accordance with the present disclosure, themapping and unmapping (mapping/unmapping) operations of the hypervisor121 may be conducted in one of multiple address mapping management modesto both improve overall system performance and maintain data integrity.

In one embodiment, the hypervisor 121 may be operated in a first addressmapping management mode, referred to herein as a rigorous mode, in whichcompletion of an unmapping for an NVS track buffer is confirmed before are-mapping of the same NVS track buffer is permitted. As explained ingreater detail below, the rigorous mode may be utilized as conditionswarrant to prevent loss of data integrity. However, as conditions changeand the rigorous mode is no longer appropriate to ensure data integrity,the hypervisor 121 may be switched to a second address mappingmanagement mode, referred to herein as a performance mode. In theperformance mode, re-mapping of the same NVS track buffer is permittedwithout first confirming that unmapping of the prior mapping of that NVStrack buffer has been completed.

The performance mode may be utilized as conditions warrant to improvesystem performance without increasing the risk of data loss. Forexample, as explained in greater detail below in connection with FIG. 7,operating conditions may be monitored and the address mapping managementmode of the hypervisor automatically switched back and forth in realtime between the rigorous and performance modes as appropriate toincrease overall system performance while maintaining data integrity inboth modes. In one embodiment, the NVS manager 119 provides anindication to the hypervisor 121 in the form of a “hint” as to whichaddress mapping management mode to utilize based upon an analysis ofcurrent conditions such as that depicted in FIG. 7, for example.

Accordingly, a determination is made (block 420, FIG. 4) as to thecurrent address mapping management mode being utilized by the hypervisor121. In response to a determination that the current address mappingmanagement mode is the rigorous mode, for example, a determination ismade (block 424) as to whether the unmapping of the NVS buffer inresponse to a dkill service request, is complete. In this example, thecache manager 113 and/or the NVS manager 119 has requested (block 416,FIG. 4) the hypervisor 121 to perform the dkill service to initiate theunmapping of the prior mapping 628 a (FIG. 6a ) of the NVS trackbuffer0.

In this embodiment, the hypervisor dkill service sets a completionindication control register to indicate completion of the dkill cacheclearance to delete the TCE table entries. In this example, uponclearance of the hypervisor cache 122, the TCE table entries for thePCIe window to NVS buffer track0 mapping 628 a will be deleted whichwill complete the unmapping of the mapping 628 a. Accordingly, thehypervisor 121 periodically polls (block 424, FIG. 4) this controlregister in the rigorous mode, to check the status of the controlregister status to determine if the unmapping of the prior mapping 628 ahas been completed.

Once the clearing of the hypervisor cache 122 has been completed andthus the unmapping of the prior NVS track buffer0 mapping 628 a has beencompleted, the control register is set to indicate completion of theunmapping. Polling of the control register detects the setting of thecontrol register and the hypervisor 121 reports to the requesting server104, 106 that the requested dkill service and thus the requestedunmapping has been completed. FIG. 5b indicates successful unmapping ofthe prior mapping 528 a by representing the mapping 528 a in theunmapped state with a dashed line arrow. In a similar manner, FIG. 6bindicates the mapping 628 a in the unmapped state with a dashed linearrow.

In one aspect of multi-mode address mapping management in accordancewith the present description, in the rigorous mode, a new mapping for anNVS track buffer is not undertaken until the unmapping of the priormapping has been confirmed. Accordingly, once the unmapping of the priormappings 528 a, 628 a, has been confirmed (block 424, FIG. 4) in therigorous mode, another mapping may be initiated for another write to thecache and NVS.

In a manner similar to that described above in connection with a writeto cache track IDO, in response to mail from a host adapter such as thehost adapter 370 a, for example, informing the cache manager 113 ofanother write request (block 428, FIG. 4) for a particular track ID suchas track ID1, for example, the cache manager 113 again allocates (block404, FIG. 4) segments 512 b (FIG. 5b ) in this example, in the cache 112for cache track ID1 of the cache address space 516 of the cache 112(FIG. 1) of the server 104. The segments 512 b are allocated for cachetrack ID1 to receive the write data identified by track identificationID1, in a DMA transfer (block 408, FIG. 4) by the cache manager 113 ofthe server 104, from the identified location within the host adapter 370a to the allocated segments 512 b (FIG. 5b ) for the cache track ID1. Inthe illustrated embodiment, the identified location of the write datafor the cache track ID1 within the host adapter 370 a, corresponds to aPCIe window identified as adapter bus window 520 b (FIG. 5b ) in thisexample, of the adapter bus address space 524. To facilitate the DMAtransfer of the write data for the cache track ID1 from the host adapter370 a to the cache 112, the cache manager causes the physical hypervisor121 (FIG. 1) to map (block 404, FIG. 4) in an address mapping 528 b(FIG. 5b ), the adapter bus window 520 b to the allocated segments 512 bfor the cache track ID1 as represented by a solid line address mappingarrow in FIG. 5 b.

In a manner similar to that described above in connection with a writeto allocated segments 604 a of NVS track buffer0, in response to themail from the host adapter 370 a informing the cache manager 113 ofanother requested write to the cache 112, the cache manager 113 alsorequests the NVS manager 119 to allocate (block 404, FIG. 4) segments(not labeled) in the NVS 118 of the NVS address space 608, for anavailable track buffer such as the track buffer0, for example. Here too,the allocation (block 404, FIG. 4) of segments for the track buffer0 isfor the next data transfer using the NVS track buffer0 rather than forthe current transfer to the NVS track buffer0. Instead, the current DMAdata transfer will utilize the segments 604 b which were previouslyallocated (FIG. 6a ) for the track buffer0 in connection with the priordata transfer using the mapping 628 a as described above.

The NVS allocated segments 604 b for the current data transfer to thetrack buffer0 receive the write data identified by track identificationID1, in a DMA transfer (block 408, FIG. 4) by the NVS manager 119 of theserver 106 from the identified location within the host adapter 370 a tothe segments 604 b allocated for the track buffer0 of the NVS addressspace 608. As previously mentioned, in this example, the identifiedlocation of the write data for track identification ID1 within the hostadapter 370 a, corresponds to the PCIe window identified as adapter buswindow 520 b in this example, of the adapter bus address space 508. Tofacilitate the DMA transfer (block 408, FIG. 4) of the ID1 write datafrom the host adapter 370 a to the NVS track buffer0, the cache manager113 and/or the NVS manager 119 informs the physical hypervisor 121 thatthe NVS destination of the ID1 write data is the NVS track buffer0 andcauses the physical hypervisor 121 (FIG. 1) to map the adapter busaddress window 520 b to the segments 604 b allocated for the currentdata transfer to the NVS track buffer0, as represented by an addressmapping 628 b (FIG. 6b ).

Because the completion of the unmapping of the prior mapping 628 a wasconfirmed (block 424, FIG. 4) in the rigorous mode before the mapping628 b was initiated (block 404, FIG. 4), the correct mapping of theadapter bus window 520 b to the previously allocated segments 604 b ofthe track buffer0 for the current data transfer of FIG. 6b is assured.Absent the rigorous mode of multi-mode address mapping management of thepresent description, the mapping 628 b (FIG. 6b ) might be initiatedbefore the unmapping of the prior mapping 628 a for the NVS trackbuffer0 is completed. For example, the hypervisor cache cleaning servicedkill may not have been completed such that the TCE table entries forthe prior mapping 628 a for the NVS track buffer0 may remain in cache121 resulting in a possible corruption of the next mapping 628 b for theNVS track buffer0 .

FIG. 6c depicts an example of a corrupted mapping 628 b′ which maps theadapter bus window 520 b to the wrong segments, that is segments 604 aof the prior data transfer, rather than the correct segments 604 b forthe current data transfer because the TCE table entries for the priormapping 628 a were not deleted from the hypervisor cache 122 prior tothe new mapping 628 b′. For example, TCE table entries for the priormapping 628 a which have not yet been deleted may indicate incorrectlythat the NVS segments currently allocated for the track buffer0 are theNVS segments 604 a instead of the correct segments 604 b, leading to theincorrect mapping 628 b′ of FIG. 6c . As a result of an incorrectmapping such as the incorrect mapping 628 b′ of FIG. 6c , an adapter buswindow such as the adapter bus window 520 b may be mapped to the wrongNVS segments resulting in a new DMA transfer being directed to the wronglocation in the NVS. In addition, prior data at that location may beincorrectly overwritten because the data may yet be needed for backuppurposes. Operating the hypervisor 121 in the rigorous mode of mappingand unmapping operations reduces or eliminates incorrect mappings whichmay result from incomplete hypervisor cache cleaning.

In one aspect of multi-mode address mapping management in accordancewith the present description, it is recognized that mapping/unmappingoperations in the rigorous mode may not always be needed to assurecorrect mappings and data integrity. More specifically, a performancemode may be employed which bypasses certain operations of the rigorousmode such as unmap completion polling, to improve system performance. Inone embodiment, mapping/unmapping operations may automatically switchback and forth between the rigorous mode and the performance mode inreal time as a function of the level of the I/O workload. For example,it is appreciated that when the I/O workload is low, the duration intime between a use of a particular NVS track buffer and a subsequentreuse of that same NVS track buffer tends to be a relatively longduration of time particularly when the NVS has a relatively large numberof available track buffers for use. It is further appreciated that thelonger the duration of time between use and subsequent reuse of aparticular NVS track buffer, the greater the opportunity for a dkilloperation to complete, cleaning the hypervisor cache 122 (FIG. 1) andcompleting the unmapping of the prior mapping of the particular NVStrack buffer before that particular track buffer is remapped again.

Thus, if the I/O workload is sufficiently low, it is appreciated thatthe unmap complete polling operation of the rigorous mode (block 424,FIG. 4) to ensure that the unmapping has been completed beforeproceeding to the next mapping, may be bypassed in a performance mode.It is noted that the unmap completion polling (block 424, FIG. 4) of therigorous mode may have a substantial adverse effect on performance.Accordingly, if the I/O workload is sufficiently low, the currentaddress mapping management mode may employ the performance mode (block420, FIG. 4) instead of the rigorous mode, such that unmap completionpolling (block 424, FIG. 4) by the hypervisor 121 may be bypassed andoperations may proceed to the next data write and next mapping (block428, FIG. 4) without waiting for the unmapping to complete. In thismanner, a substantial performance gain may be obtained in theperformance mode without sacrificing data integrity.

Conversely, if the I/O workload is sufficiently high, it is appreciatedthat the unmap completion polling operation of the rigorous mode (block424, FIG. 4) may be appropriate to ensure that the unmapping has beencompleted before proceeding to the next mapping. Accordingly, if the I/Oworkload is sufficiently high, the current address mapping managementmode may employ the rigorous mode (block 420, FIG. 4) instead of theperformance mode, and the unmap completion polling (block 424, FIG. 4)of the rigorous mode may be utilized. As a result, in the rigorous mode,operations do not proceed to the next data write (block 428, FIG. 4)without first waiting for the unmapping to complete (block 424, FIG. 4).Consequently, data integrity may be maintained notwithstandingrelatively high levels of I/O workload.

It is appreciated that the level of I/O workload may be monitored andmeasured using a variety of techniques for purposes of automaticallyselecting an appropriate address mapping management mode as a functionof I/O workload level. In one embodiment, the number of free NVS trackbuffers may be monitored and an address mapping management mode may beautomatically selected as a function of the current number of free NVStrack buffers.

For example, in the illustrated embodiment, the system may have eightbays in which each bay houses host adapters 370 and device adapters 340,350. In one embodiment, the NVS has 300 track buffers for each bay or2400 track buffers in total. If a particular bay runs out of availabletrack buffers to be mapped to that bay, track buffers normally mapped toanother bay may be mapped to that bay.

In one technique for selecting an address mapping management mode, ifmonitoring determines that the number of available track buffers hasfallen below a certain threshold, such as below 50 available trackbuffers out of a total of 2400 track buffers in this example, the NVSmanager may issue a hint to the hypervisor 121 to operate its addressmapping management operations as depicted in FIG. 4 in the rigorousmode. Conversely, if monitoring determines that the number of availabletrack buffers has risen above a certain higher threshold, such as above300 available track buffers out of a total of 2400 track buffers in thisexample, the NVS manager may issue a hint to the hypervisor 121 tooperate its address mapping management operations as depicted in FIG. 4in the performance mode.

It is appreciated that the number of track buffers utilized by an NVSand the number and magnitude of thresholds utilized to select an addressmapping management mode, may vary depending upon the particularapplication. It is further appreciated that other criteria may bemonitored for purposes of selecting an address mapping management mode.For example, the number of dkill operations issued or the duration oftime since a particular track buffer was utilized, may be monitored todetermine whether an adequate unmapping opportunity has been afforded toensure that the unmapping of the prior mapping of that track buffer hasbeen completed before that track buffer is reused, and an appropriateaddress mapping management mode selected. Other criteria may bemonitored for purposes of selecting an address mapping management mode,depending upon the particular application.

FIG. 7 depicts one example of operations for which of one or more of thecache manager 113 (FIG. 1), NVS manager 119 and physical hypervisor 121have been configured to automatically select an address mappingmanagement mode as a function of the number of available NVS trackbuffers. In this example, a wait time is implemented which can reducethe frequency of changing between modes. Although the logic performingthe operations of FIG. 7 is described in connection with the cachemanager 113 (FIG. 1), NVS manager 119 and/or physical hypervisor 121 inthe illustrated embodiment, it is appreciated that logic performing suchmanagement operations may be located in fewer devices or in otherdevices, depending upon the particular application.

More particularly, the quantity of free NVS track buffers is monitored(block 704, FIG. 7) and if the level of free NVS track buffers isdetermined (block 708, FIG. 7) to fall below a first threshold (such as50 free NVS track buffers, for example), the rigorous mode may beselected or continued (block 712, FIG. 7). If the selection of therigorous mode constitutes a switch from the performance mode, in oneembodiment, the NVS manager 119 can provide a hint to the hypervisor 121to switch the mapping/unmapping operations depicted in FIG. 4 to therigorous mode.

Conversely, if the level of free NVS track buffers is determined (block708, FIG. 7) to have not fallen below the first threshold (such as 50free NVS track buffers, for example), in other words, it is determined(block 708, FIG. 7) that the level of free NVS track buffers remainsabove the first threshold (such as 50 free NVS track buffers, forexample), another determination (block 716, FIG. 7) is made to determineif the level of free NVS track buffer remains above a second, higherthreshold (such as 300 free NVS track buffers, for example). If not, therigorous mode is selected or continued (block 712, FIG. 7). Again, ifthe selection of the rigorous mode constitutes a switch from theperformance mode, in one embodiment, the NVS manager 119 can provide ahint to the hypervisor 121 to switch the mapping/unmapping operationsdepicted in FIG. 4 to the rigorous mode.

Alternatively, if it is determined (block 716, FIG. 7) that the level offree NVS track buffer is currently above the second threshold (such as300 free NVS track buffers, for example), another determination (block720, FIG. 7) is made as to whether the mapping/unmapping operation ofthe hypervisor 121 is currently in the rigorous mode. If not, that is itis determined that the mapping/unmapping operation is currently in theperformance mode, the performance mode is continued (block 738, FIG. 7).Conversely, after determining (block 716, FIG. 7) that the level of freeNVS track buffer is currently above the second threshold (such as 300free NVS track buffers, for example), and it is determined (block 720,FIG. 7) that the mapping/unmapping operation of the hypervisor 121 iscurrently in the rigorous mode, a timer is started/restarted (block 724,FIG. 7) to time a predetermined interval of wait time.

A determination is made (block 728, FIG. 7) as to whether the timer hasexpired. If so, it is determined that the level of free NVS trackbuffers has remained above the second threshold for at least thepredetermined interval of wait time. Accordingly, the mapping/unmappingoperation of the hypervisor 121 is switched (block 738, FIG. 7) from therigorous mode to the performance mode. In this manner, a wait time isimposed before switching from the rigorous mode to the performance modeto avoid an excessive frequency of mode switching. Here too, the NVSmanager 119 can in one embodiment, provide a hint to the hypervisor 121to switch to the performance mode.

Conversely, if it is determined (block 728, FIG. 7) that the timer hasnot expired, monitoring of the quantity of free NVS track buffers iscontinued (block 732, FIG. 7). If at any time during the wait timinginterval being timed, it is determined (block 734, FIG. 7) that thelevel of free NVS track buffers has fallen below the second threshold,the wait timer interval is restarted (block 724, FIG. 7) and theoperations of blocks 728-738 are repeated. On the other hand, if isdetermined (block 734, FIG. 7) that the level of free

NVS track buffers has remained above the second threshold for the entireduration (block 728, FIG. 7) of the wait timing interval, in otherwords, the wait timing interval has expired (block 728, FIG. 7) whilethe level of free NVS track buffers has remained above (block 734, FIG.7) the second threshold, the mapping/unmapping operation of thehypervisor 121 is switched (block 738, FIG. 7) from the rigorous mode tothe performance mode. Again, the wait time is imposed before switchingfrom the rigorous mode to the performance mode to avoid an excessivefrequency of mode switching. Here too, the NVS manager 119 can provide ahint to the hypervisor to switch to the performance mode.

It is appreciated that the such a wait interval is optional and may beprovided before switching between other modes. Moreover, it isappreciated that the number of thresholds, and the magnitude of eachthreshold may vary, depending upon the particular application. Otheraddress mapping management modes may be utilized, depending upon theparticular application.

In the illustrated embodiment, the storage manager of the storagecontroller 102 implementing multi-mode address mapping management inaccordance with the present description, is depicted as software storedin a memory and executed by a processor of the storage controller.However, it is appreciated that the multi-mode address mappingmanagement logic functions, may be implemented as hardware, software,firmware or any combination of one or more thereof, depending upon theparticular application. In addition, logic functions of multi-modeaddress mapping management may be implemented in a host or storage inaddition to or instead of a storage controller.

In certain embodiments, the memories 112, 114, 116, 118 may comprise ahigh cost and very low latency device such as a Dynamic Random AccessMemory (DRAM) or Static Random Access Memory (SRAM), and less expensiveand higher latency and higher capacity storage devices such asnon-volatile random access memory (NVRAM), including MagnetoresistiveRandom Access Memory (MRAM), Phase Change Memory (PCM), Resistive RandomAccess Memory (RRAM), spin transfer torque memory (STM-RAM), conductivebridging RAM (CBRAM), NAND memory devices, such as flash memory andsolid state drives (SSDs), etc. In certain embodiments, the memories112, 114, 116, 118 may have different endurance profiles with differentnumber of available erase cycles, such that higher levels of thememories 112, 114, 116, 118 allow for a greater number of erase cycles,i.e., greater endurance, than the lower levels of the memories 112, 114,116, 118.

The storage 101 may comprise one or more storage devices known in theart, such as a solid state storage device (SSD), magnetic hard diskdrive, optical disk, tape, etc. The storage devices may further beconfigured into an array of devices, such as Just a Bunch of Disks(JBOD), Direct Access Storage Device (DASD), Redundant Array ofIndependent Disks (RAID) array, virtualization device, etc. Further, thestorage devices may comprise heterogeneous storage devices fromdifferent vendors or from the same vendor.

The storage devices of the storage 101 may be configured to store datain units or subunits of data storage such as tracks, extents, blocks,pages, segments, cylinders, volumes, etc. Although multi-mode addressmapping management in accordance with the present description aredescribed in connection with storage units such as tracks, it isappreciated that multi-mode address mapping management in accordancewith the present description is applicable to other storage units andsubunits such as sectors, cylinders, volumes, extents, blocks, pages,segments, etc.

The network 111 may comprise a Storage Area Network (SAN), a Local AreaNetwork (LAN), a Wide Area Network (WAN), the Internet, and Intranet,etc. Alternatively, the hosts 108 . . . 110 may connect to the storagecontroller 102 over a bus interface, such as a Peripheral ComponentInterconnect (PCI) bus interface and other interfaces known in the art.

The computational components of the figures may each be implemented inone or more computer systems, such as the computer system 1002 shown inFIG. 8.

The computer system 1002 may be a computer system, which is operationalwith numerous other general purpose or special purpose computing systemenvironments or configurations. Examples of well-known computingsystems, environments, and/or configurations that may be suitable foruse with computer system 1002 include, but are not limited to, personalcomputer systems, server computer systems, thin clients, thick clients,handheld or laptop devices, multiprocessor systems, microprocessor-basedsystems, set top boxes, programmable consumer electronics, network PCs,minicomputer systems, mainframe computer systems, and distributed cloudcomputing environments that include any of the above systems or devices,and the like.

Computer system/server 1002 may be described in the general context ofcomputer system executable instructions, such as program modules, beingexecuted by a computer system. Generally, program modules may includeroutines, programs, objects, components, logic, data structures, and soon that perform particular tasks or implement particular abstract datatypes. Computer system/server 1002 may be practiced in distributed cloudcomputing environments where tasks are performed by remote processingdevices that are linked through a communications network. In adistributed cloud computing environment, program modules may be locatedin both local and remote computer system storage media including memorystorage devices.

As shown in FIG. 8, the computer system/server 1002 is shown in the formof a general-purpose computing device. The components of computersystem/server 1002 may include, but are not limited to, one or moreprocessors or processing units 1004, a system memory 1006, and a bus1008 that couples various system components including system memory 1006to processor 1004. Bus 1008 represents one or more of any of severaltypes of bus structures, including a memory bus or memory controller, aperipheral bus, an accelerated graphics port, and a processor or localbus using any of a variety of bus architectures. By way of example, andnot limitation, such architectures include Industry StandardArchitecture (ISA) bus, Micro Channel Architecture (MCA) bus, EnhancedISA (EISA) bus, Video Electronics Standards Association (VESA) localbus, and Peripheral Component Interconnects (PCI) bus.

Computer system/server 1002 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 1002, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 1006 can include computer system readable media in theform of volatile memory, such as random access memory (RAM) 1010 and/orcache memory 1012. Computer system/server 1002 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 1013 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”).

Although not shown, a magnetic disk drive for reading from and writingto a removable, non-volatile magnetic disk (e.g., a “floppy disk”), andan optical disk drive for reading from or writing to a removable,non-volatile optical disk such as a CD-ROM, DVD-ROM or other opticalmedia can be provided. In such instances, each can be connected to bus1008 by one or more data media interfaces. As will be further depictedand described below, memory 1006 may include at least one programproduct having a set (e.g., at least one) of program modules that areconfigured to carry out the functions of embodiments of the invention.

Program/utility 1014, having a set (at least one) of program modules1016, may be stored in memory 1006 by way of example, and notlimitation, as well as an operating system, one or more applicationprograms, other program modules, and program data. Each of the operatingsystem, one or more application programs, other program modules, andprogram data or some combination thereof, may include an implementationof a networking environment. The components of the computer system 1002may be implemented as program modules 1016 which generally carry out thefunctions and/or methodologies of embodiments of the invention asdescribed herein. The system of FIG. 1 may be implemented in one or morecomputer systems 1002, where if they are implemented in multiplecomputer systems 1002, then the computer systems may communicate over anetwork.

Computer system/server 1002 may also communicate with one or moreexternal devices 1018 such as a keyboard, a pointing device, a display1020, etc.; one or more devices that enable a user to interact withcomputer system/server 1002; and/or any devices (e.g., network card,modem, etc.) that enable computer system/server 1002 to communicate withone or more other computing devices. Such communication can occur viaInput/Output (I/O) interfaces 1022. Still yet, computer system/server1002 can communicate with one or more networks such as a local areanetwork (LAN), a general wide area network (WAN), and/or a publicnetwork (e.g., the Internet) via network adapter 1024. As depicted,network adapter 1024 communicates with the other components of computersystem/server 1002 via bus 1008. It should be understood that althoughnot shown, other hardware and/or software components could be used inconjunction with computer system/server 1002. Examples, include, but arenot limited to microcode, device drivers, redundant processing units,external disk drive arrays, RAID systems, tape drives, and data archivalstorage systems, etc.

The reference characters used herein, such as i, j, and n, are used todenote a variable number of instances of an element, which may representthe same or different values, and may represent the same or differentvalue when used with different or the same elements in differentdescribed instances.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out processoroperations in accordance with aspects of the present invention.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Java, Smalltalk, C++ or the like,and conventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terms “an embodiment”, “embodiment”, “embodiments”, “theembodiment”, “the embodiments”, “one or more embodiments”, “someembodiments”, and “one embodiment” mean “one or more (but not all)embodiments of the present invention(s)” unless expressly specifiedotherwise.

The terms “including”, “comprising”, “having” and variations thereofmean “including but not limited to”, unless expressly specifiedotherwise.

The enumerated listing of items does not imply that any or all of theitems are mutually exclusive, unless expressly specified otherwise.

The terms “a”, “an” and “the” mean “one or more”, unless expresslyspecified otherwise.

Devices that are in communication with each other need not be incontinuous communication with each other, unless expressly specifiedotherwise. In addition, devices that are in communication with eachother may communicate directly or indirectly through one or moreintermediaries.

A description of an embodiment with several components in communicationwith each other does not imply that all such components are required. Onthe contrary a variety of optional components are described toillustrate the wide variety of possible embodiments of the presentinvention.

When a single device or article is described herein, it will be readilyapparent that more than one device/article (whether or not theycooperate) may be used in place of a single device/article. Similarly,where more than one device or article is described herein (whether ornot they cooperate), it will be readily apparent that a singledevice/article may be used in place of the more than one device orarticle or a different number of devices/articles may be used instead ofthe shown number of devices or programs. The functionality and/or thefeatures of a device may be alternatively embodied by one or more otherdevices which are not explicitly described as having suchfunctionality/features. Thus, other embodiments of the present inventionneed not include the device itself.

The foregoing description of various embodiments of the invention hasbeen presented for the purposes of illustration and description. It isnot intended to be exhaustive or to limit the invention to the preciseform disclosed. Many modifications and variations are possible in lightof the above teaching. It is intended that the scope of the invention belimited not by this detailed description, but rather by the claimsappended hereto. The above specification, examples and data provide acomplete description of the manufacture and use of the composition ofthe invention. Since many embodiments of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims herein after appended.

What is claimed is:
 1. A computer program product, the computer programproduct comprising a computer readable storage medium having programcode embodied therewith, the program code executable by at least oneprocessor to perform operations, the operations comprising: addressmapping in a selected address mapping management mode, a selected dataunit buffer of a storage controller and a selected adapter coupled tothe storage controller, for a first data transfer between an addressmapped data unit buffer and an address mapped adapter; upon completionof the first data transfer, initiating unmapping of the address mappeddata unit buffer and the address mapped adapter of the first datatransfer in the selected address mapping management mode; in response tothe selected address mapping management mode being in a first addressmapping management mode, confirming that the initiated unmapping of theaddress mapped data unit buffer and the address mapped adapter of thefirst data transfer is complete prior to again initiating addressmapping a selected data unit buffer of the storage controller and aselected adapter coupled to the storage controller, for a second datatransfer between an addressed mapped data unit buffer and an addressedmapped adapter; and in response to the selected address mappingmanagement mode being in a second address mapping management mode, againinitiating address mapping a selected data unit buffer of the storagecontroller and a selected adapter coupled to the storage controller, fora second data transfer between an address mapped data unit buffer and anaddress mapped adapter, without confirming that the initiated unmappingof the address mapped data unit buffer and the address mapped adapter ofthe first data transfer is complete so that confirming that theinitiated unmapping of the address mapped data unit buffer and theaddress mapped adapter of the first data transfer is complete, isbypassed prior to again initiating address mapping a selected data unitbuffer of the storage controller and a selected adapter.
 2. The computerprogram product of claim 1, wherein the operations further comprise:freeing data unit buffers after completion of data transfers to thosedata unit buffers to be available for an additional data transfer toeach free data unit buffer; monitoring a level of free data unit buffersavailable for an additional data transfer; comparing the level of freedata unit buffers to a first threshold level; and in response todetermining that the level of free data unit buffers is below the firstthreshold level, selecting the first address mapping management mode. 3.The computer program product of claim 2, wherein the operations furthercomprise: monitoring the level of free data unit buffers available foran additional data transfer; comparing the level of free data unitbuffers to a second threshold level; and in response to determining thatthe level of free data unit buffers is above the second threshold level,selecting the second address mapping management mode.
 4. The computerprogram product of claim 3, wherein the operations further comprise: inresponse to determining the level of free data unit buffers to be abovethe second threshold level, determining a current selected addressmapping management mode; and in response to determining that the currentselected address mapping management mode is the first address mappingmanagement mode, starting a timer to start timing a first wait periodprior to selecting the second address mapping management mode.
 5. Thecomputer program product of claim 4, wherein the operations furthercomprise: determining during the first wait period whether the level offree data unit buffers remains above the second threshold level; inresponse to determining that the level of free data unit buffers remainsabove the second threshold level during the first wait period,performing said selecting the second address mapping management mode;and in response to determining that the level of free data unit buffershas fallen below the second threshold level during the first waitperiod, continuing in the first address mapping management mode.
 6. Thecomputer program product of claim 5, wherein the operations furthercomprise: in response to determining that the level of free data unitbuffers has fallen below the second threshold level during the firstwait period, restarting the timer to start timing a second wait period;determining during the second wait period whether the level of free dataunit buffers rises above the second threshold level; in response todetermining that the level of free data unit buffers remains above thesecond threshold level during the second wait period, performing saidselecting the second address mapping management mode; and in response todetermining that the level of free data unit buffers has fallen belowthe second threshold level during the second wait period, continuing inthe first address mapping management mode.
 7. The computer programproduct of claim 1 wherein an address mapped adapter associated with aparticular data transfer is coupled to one of a storage and a host sothat the particular data transfer transfers data between the one of thestorage and host coupled to the associated address mapped adapter, andan address mapped data unit buffer associated with the particular datatransfer.
 8. A system, comprising: a host; storage; and a storagecontroller configured to control the storage, the storage controllerhaving one or more processors, one or more computer-readable memoriesincluding a cache and nonvolatile storage (NVS) having a plurality ofdata unit buffers, one or more computer-readable, tangible storagedevices, a plurality of adapters coupling the storage controller to ahost and to storage; a hypervisor configured for address mapping betweena selected adapter and a selected memory, and program instructions,stored on at least one of the one or more computer-readable, tangiblestorage devices for execution by at least one of the one or moreprocessors via at least one of the one or more memories, to performoperations, the operations comprising: address mapping in a selectedaddress mapping management mode, a selected data unit buffer of thestorage controller and a selected adapter coupled to the storagecontroller, for a first data transfer between an address mapped dataunit buffer and an address mapped adapter; upon completion of the firstdata transfer, initiating unmapping of the address mapped data unitbuffer and the address mapped adapter of the first data transfer in theselected address mapping management mode; in response to the selectedaddress mapping management mode being in a first address mappingmanagement mode, confirming that the initiated unmapping of the addressmapped data unit buffer and the address mapped adapter of the first datatransfer is complete prior to again initiating address mapping aselected data unit buffer of the storage controller and a selectedadapter coupled to the storage controller, for a second data transferbetween an addressed mapped data unit buffer and an addressed mappedadapter; and in response to the selected address mapping management modebeing in a second address mapping management mode, again initiatingaddress mapping a selected data unit buffer of the storage controllerand a selected adapter coupled to the storage controller, for a seconddata transfer between an address mapped data unit buffer and anaddressed mapped adapter, without confirming that the initiatedunmapping of the address mapped data unit buffer and the address mappedadapter of the first data transfer is complete so that confirming thatthe initiated unmapping of the address mapped data unit buffer and theaddress mapped adapter of the first data transfer is complete, isbypassed prior to again initiating address mapping a selected data unitbuffer of the storage controller and a selected adapter.
 9. The systemof claim 8, wherein the operations further comprise: freeing data unitbuffers after completion of data transfers to those data unit buffers tobe available for an additional data transfer to each free data unitbuffer; monitoring a level of free data unit buffers available for anadditional data transfer; comparing the level of free data unit buffersto a first threshold level; and in response to determining that thelevel of free data unit buffers is below the first threshold level,selecting the first address mapping management mode.
 10. The system ofclaim 9, wherein the operations further comprise: monitoring the levelof free data unit buffers available for an additional data transfer;comparing the level of free data unit buffers to a second thresholdlevel; and in response to determining that the level of free data unitbuffers is above the second threshold level, selecting the secondaddress mapping management mode.
 11. The system of claim 10, wherein theoperations further comprise: in response to determining the level offree data unit buffers to be above the second threshold level,determining a current selected address mapping management mode; and inresponse to determining that the current selected address mappingmanagement mode is the first address mapping management mode, starting atimer to start timing a first wait period prior to selecting the secondaddress mapping management mode.
 12. The system of claim 11, wherein theoperations further comprise: determining during the first wait periodwhether the level of free data unit buffers remains above the secondthreshold level; in response to determining that the level of free dataunit buffers remains above the second threshold level during the firstwait period, performing said selecting the second address mappingmanagement mode; and in response to determining that the level of freedata unit buffers has fallen below the second threshold level during thefirst wait period, continuing in the first address mapping managementmode.
 13. The system of claim 12, wherein the operations furthercomprise: in response to determining that the level of free data unitbuffers has fallen below the second threshold level during the firstwait period, restarting the timer to start timing a second wait period;determining during the second wait period whether the level of free dataunit buffers rises above the second threshold level; in response todetermining that the level of free data unit buffers remains above thesecond threshold level during the second wait period, performing saidselecting the second address mapping management mode; and in response todetermining that the level of free data unit buffers has fallen belowthe second threshold level during the second wait period, continuing inthe first address mapping management mode.
 14. A computer-implementedmethod, comprising: address mapping in a selected address mappingmanagement mode, a selected data unit buffer of a storage controller anda selected adapter coupled to the storage controller, for a first datatransfer between an address mapped data unit buffer and an addressedmapped adapter; upon completion of the first data transfer, initiatingunmapping of the address mapped data unit buffer and the address mappedadapter of the first data transfer in the selected address mappingmanagement mode; in response to the selected address mapping managementmode being in a first address mapping management mode, confirming thatthe initiated unmapping of the address mapped data unit buffer and theaddress mapped adapter of the first data transfer is complete prior toagain initiating address mapping a selected data unit buffer of thestorage controller and a selected adapter coupled to the storagecontroller, for a second data transfer between an addressed mapped dataunit buffer and an addressed mapped adapter; and in response to theselected address mapping management mode being in a second addressmapping management mode, again initiating address mapping a selecteddata unit buffer of the storage controller and a selected adaptercoupled to the storage controller, for a second data transfer between anaddress mapped data unit buffer and an addressed mapped adapter, withoutconfirming that the initiated unmapping of the address mapped data unitbuffer and the address mapped adapter of the first data transfer iscomplete so that confirming that the initiated unmapping of the addressmapped data unit buffer and the address mapped adapter of the first datatransfer is complete, is bypassed prior to again initiating addressmapping a selected data unit buffer of the storage controller and aselected adapter.
 15. The method of claim 14, further comprising:freeing data unit buffers after completion of data transfers to thosedata unit buffers to be available for an additional data transfer toeach free data unit buffer; monitoring a level of free data unit buffersavailable for an additional data transfer; comparing the level of freedata unit buffers to a first threshold level; and in response todetermining that the level of free data unit buffers is below the firstthreshold level, selecting the first address mapping management mode.16. The method of claim 15, further comprising: monitoring the level offree data unit buffers available for an additional data transfer;comparing the level of free data unit buffers to a second thresholdlevel; and in response to determining that the level of free data unitbuffers is above the second threshold level, selecting the secondaddress mapping management mode.
 17. The method of claim 16, furthercomprising: in response to determining the level of free data unitbuffers to be above the second threshold level, determining a currentselected address mapping management mode; and in response to determiningthat the current selected address mapping management mode is the firstaddress mapping management mode, starting a timer to start timing afirst wait period prior to selecting the second address mappingmanagement mode.
 18. The method of claim 17, further comprising:determining during the first wait period whether the level of free dataunit buffers remains above the second threshold level; in response todetermining that the level of free data unit buffers remains above thesecond threshold level during the first wait period, performing saidselecting the second address mapping management mode; and in response todetermining that the level of free data unit buffers has fallen belowthe second threshold level during the first wait period, continuing inthe first address mapping management mode.
 19. The method of claim 18,further comprising: in response to determining that the level of freedata unit buffers has fallen below the second threshold level during thefirst wait period, restarting the timer to start timing a second waitperiod; determining during the second wait period whether the level offree data unit buffers rises above the second threshold level; inresponse to determining that the level of free data unit buffers remainsabove the second threshold level during the second wait period,performing said selecting the second address mapping management mode;and in response to determining that the level of free data unit buffershas fallen below the second threshold level during the second waitperiod, continuing in the first address mapping management mode.
 20. Themethod of claim 14 wherein an address mapped adapter associated with aparticular data transfer is coupled to one of a storage and a host sothat the particular data transfer transfers data between the one of thestorage and host coupled to the associated address mapped adapter, andan address mapped data unit buffer associated with the particular datatransfer.